#include <stdio.h>
// 函数定义
float add(float x, float y)
{
    return x + y;
}

int main(void)
{ 
   float a, b, c;
   printf("Please enter a and b:");   
   scanf("%f%f",&a, &b);              
   // 函数调用
   c = add(a,b);                       
   printf("sum is %f\n", c);   
   return 0;
}